Super junction power device and method of making the same

ABSTRACT

The present invention provides a power device with super junction structure (or referred to as super junction power device) and a method of making the same. When making a super junction power device, impurity of a second conductive type may be implanted into an epitaxial layer of a first conductive type to form a floating island of the second conductive type and a pillar of the second conductive type successively through a super junction mask (or reticle) after forming the epitaxial layer of the first conductive type, directly through a well mask (or reticle) before or after forming a well of the second conductive type, and directly through a contact mask (or reticle) before or after forming a contact structure. Multiple epitaxial processes and deep trench etching process may not be needed. Therefore, the process is simple, the cost is low and yield and reliability are high. Because the super junction power device of the present invention has both the floating island of the second conductive type and the pillar of the second conductive type, in open state, a breakdown voltage may be raised and both Miller capacitance and input capacitance can be decreased and in on state, an on-state resistance can be decreased.

FIELD OF THE INVENTION

The present invention belongs to semiconductor device technology, andrelates to a super junction power device and a method of making thesame.

BACKGROUND OF THE INVENTION

In the field of power device, VDMOSFET (Vertical Double Diffused MetalOxide Semiconductor Field Effect Transistor) is widely applied becauseof its advantages such as high operating frequency, good thermalstability and simple driving circuit. The two most important parametersfor a power device among all are the breakdown voltage (BV) andon-resistance (Ron). A popular design of a power device on these twoparameters is to provide high enough BV and low Ron as well to decreasepower consumption.

Improvement of performance of a traditional power device was held backbecause of the tradeoff of BV and Ron on each other. Therefore, a superjunction was introduced into a drift region of a traditional VDMOSFET toform a super junction structure in power MOSFET (referred to as SJMOS)to optimize the relation between BV and Ron to show advantages such assmall Ron, fast turning on and low switch consumption which draw theindustry's attention.

Current method of a super junction structure is generally formed by adeep trench etching process and a filling process in an epitaxial layeror formed by an epitaxial process and an implantation of doping in theepitaxial layer for multiple times so as to increase BV due to chargesharing effect. Then, the doping concentration of the epitaxial layermay be significantly increased at on-state to achieve lower Ron; theequivalent doping concentration in epi layer at off-state can be keptthe same (due to the charge sharing effect) to achieve same BV. However,when the super junction is formed with the deep trench etching andfilling process in the epitaxial layer, the deep trench may result instress, poor defects and uniformity problems, and in turn degradingyield and reliability. The deeper the deep trench leads to larger aspectratio of trench and more difficulty filling back and implant doseaccuracy (for precision charge sharing) to achieve a higher BV.Additionally, the formation process is complicate and higher cost whenthe super junction is formed by performing multiple epitaxial andimplant of doping in the epitaxial layer. Therefore, it is needed toprovide a better super junction power device and method of making thesame.

SUMMARY OF THE INVENTION

In light of above-mentioned drawbacks of the current technology, anobject of the present invention is to provide a super junction powerdevice and a method of making the same to solve the problems of stress,defect and uniformity and the problems of complicate processes and highcost.

To implement above-mentioned object and other related objects, thepresent invention provides a method of making a super junction powerdevice, comprising steps of:

forming an epitaxial layer of a first conductive type;

forming trench gate structures in the epitaxial layer of the firstconductive type, the trench gate structures comprising a gate oxidelayer and a gate conductive layer;

through a well mask, forming a well of a second conductive type in theepitaxial layer of the first conductive type between the trench gatestructures;

through a source mask, forming a source of the first conductive type inthe well of the second conductive type;

through a contact mask, forming a contact structure passing through thesource of the first conductive type and in mutual contact with the wellof the second conductive type;

forming a floating island of the second conductive type, positioning inthe epitaxial layer of the first conductive type, and a top surface anda bottom surface of the floating island of the second conductive typebeing in mutual contact with the epitaxial layer of the first conductivetype;

forming a pillar of the second conductive type, positioning in theepitaxial layer of the first conductive type and right above thefloating island of the second conductive type, and being in mutualcontact with the well of the second conductive type.

Optionally, a super junction mask is used for implanting the dopingimpurity of the second conductive type into the epitaxial layer of thefirst conductive type to form the floating island of the secondconductive type and the pillar of the second conductive typesuccessively.

Optionally, before or after forming the well of the second conductivetype, through the well mask, impurity of the second conductive type isimplanted into the epitaxial layer of the first conductive type to formthe floating island of the second conductive type and the pillar of thesecond conductive type successively.

Optionally, before or after forming the contact structure, through thecontact mask, impurity of the second conductive type is implanted intothe epitaxial layer of the first conductive type to form the floatingisland of the second conductive type and the pillar of the secondconductive type successively.

Optionally, a thickness range of the epitaxial layer of the firstconductive type between the formed floating island of the formed secondconductive type and the pillar of the second conductive type is greaterthan 0.1 μm.

Optionally, the step of forming a contact structure may comprise:

through the contact mask, etching the source of the first conductivetype and forming a contact trench passing through the source of thefirst conductive type;

through the contact mask, implanting impurity of the second conductivetype into the c to form a contact region of the second conductive type;

through the contact mask, forming a metal contact region filling in thecontact trench, and the metal contact region being in mutual contactwith the contact region of the second conductive type.

Optionally, the first conductive type is n type, and the secondconductive type is p type; or the first conductive type is p type, andthe second conductive type is n type.

Optionally, the method may further comprise a step of forming a bufferlayer of the first conductive type at the bottom surface of theepitaxial layer of the first conductive type.

Optionally, the method may further comprise a step of forming animplanted layer of the second conductive type at the bottom surface ofthe epitaxial layer of the first conductive type.

The present invention further provides a super junction power device,characterized by, the super junction power device comprising:

an epitaxial layer of a first conductive type;

a well of a second conductive type, positioning in the epitaxial layerof the first conductive type;

a source of the first conductive type, positioning in the well of thesecond conductive type;

trench gate structures, comprising a gate oxide layer and a gateconductive layer, the trench gate structures being positioned in theepitaxial layer of the first conductive type and passing through thesource of the first conductive type and the well of a second conductivetype;

a contact structure, passing through the source of the first conductivetype and in mutual contact with the well of the second conductive type;

a floating island of the second conductive type, positioning in theepitaxial layer of the first conductive type, and a top surface and abottom surface of the floating island of the second conductive typebeing in mutual contact with the epitaxial layer of the first conductivetype;

a pillar of the second conductive type, positioning in the epitaxiallayer of the first conductive type and right above the floating islandof the second conductive type, and being in mutual contact with the wellof the second conductive type.

Optionally, a width of the floating island of the second conductive typeis the same as that of the pillar of the second conductive type.

Optionally, a thickness range of the epitaxial layer of the firstconductive type between the floating island of the second conductivetype and the pillar of the second conductive type is greater than 0.1μm.

Optionally, the contact structure comprises a metal contact region, themetal contact region is positioned at a contact region of the secondconductive type in the well of the second conductive type, passingthrough the source of the first conductive type and in mutual contactwith the contact region of the second conductive type.

Optionally, the first conductive type is n type, and the secondconductive type is p type; or the first conductive type is p type, andthe second conductive type is n type.

Optionally, the super junction power device may further comprise abuffer layer of the first conductive type at the bottom surface of theepitaxial layer of the first conductive type.

Optionally, the super junction power device may further comprise animplanted layer of the second conductive type at the bottom surface ofthe epitaxial layer of the first conductive type.

As mentioned above, the super junction power device and the method ofmaking the same of the present invention produce effects of:

When making a super junction power device, impurity of a secondconductive type may be implanted into an epitaxial layer of a firstconductive type to form a floating island of the second conductive typeand a pillar of the second conductive type successively through adding asuper junction mask after forming the epitaxial layer of the firstconductive type, directly through a well mask before or after forming awell of the second conductive type, and directly through a contact maskbefore or after forming a contact structure. The conventional method byusing multiple epitaxial growth and deep trench etching process may notbe effective, the new method to form super junction structure is simple,the cost is low and the yield and reliability can be high.

The super junction power device of the present invention has both thefloating islands of the second conductive type and the pillars of thesecond conductive type. In open state (or off-state), a breakdownvoltage may be raised and both Miller capacitance and input capacitancemay be decreased because both the floating islands of the secondconductive type and the pillars of the second conductive type facilitatethe charge sharing effect in a drift region of the epitaxial layer ofthe first conductive type. In on state, both the floating islands of thesecond conductive type and the pillars of the second conductive type canallow the drift region in the epitaxial layer of the first conductivetype having higher doping concentration to significantly conduct acurrent and decrease an on-state resistance of a VDMOSFET device.Further, because the epitaxial layer of the first conductive type ispositioned between the floating islands of the second conductive typeand the pillars of the second conductive type, an additional triode(i.e. bipolar transistor) may be formed in the epitaxial layer of thefirst conductive type to further decrease the on-state resistance of aIGBT device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a process flow chart of forming a super junction powerdevice according to the present invention.

FIG. 2 shows a process flow chart of forming a super junction powerdevice according to a first embodiment.

FIG. 3 shows a perspective view of a structure of a super junction powerdevice according to the first embodiment.

FIG. 4 shows a perspective view of a structure of a super junctionVDMOSFET device according to the first embodiment.

FIG. 5 shows a perspective view of a structure of a super junction IGBTdevice according to the first embodiment.

FIG. 6 shows a process flow chart of forming a super junction powerdevice according to a second embodiment.

FIG. 7 shows a perspective view of a structure of a super junction powerdevice according to a second embodiment.

FIG. 8 shows a perspective view of a structure of a super junctionVDMOSFET device according to the second embodiment.

FIG. 9 shows a perspective view of a structure of a super junction IGBTdevice according to the second embodiment.

FIG. 10 shows a process flow chart of forming a super junction powerdevice according to a third embodiment.

FIG. 11 shows a perspective view of a structure of a super junctionpower device according to the third embodiment.

FIG. 12 shows a perspective view of a structure of a super junctionVDMOSFET device according to the third embodiment.

FIG. 13 shows a perspective view of a structure of a super junction IGBTdevice according to the third embodiment.

REFERENCE SIGNS

-   -   101, 201, 301 a substrate of a first conductive type    -   102, 202, 302 an epitaxial layer of the first conductive type    -   103, 203, 303 a well of a second conductive type    -   104, 204, 304 a source of the first conductive type    -   105, 205, 305 a contact structure    -   3051 a contact region of the second conductive type    -   3052 a metal contact region    -   106, 206, 306 a floating island of the second conductive type    -   107, 207, 307 a pillar of the second conductive type    -   108, 208, 308 a gate oxide layer    -   109, 209, 309 a gate conductive layer    -   110, 210, 310 an interlayer dielectric layer    -   111, 211, 311 a source metal layer    -   112, 212, 312 a drain metal layer    -   113, 213, 313 an implanted layer of the second conductive type    -   314 a buffer layer of the first conductive type

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Reference is now made to the following concrete examples taken inconjunction with the accompanying drawings to illustrate implementationof the present invention. Persons of ordinary skill in the art havingthe benefit of the present disclosure will understand other advantagesand effects of the present invention. The present invention may beimplemented with other examples. For various view or application,details in the present disclosure may be used for variation or changefor implementing embodiments within the scope of the present invention.

Please refer to FIGS. 1 to 13 . Please note that the drawings providedhere are only for examples but not limited to the specific number orscale shown therein. When implementing the examples according to thedrawings, condition, number and proportion of each element may bechanged and arrangement of the elements may be in a more complex way.

Please refer to FIG. 1 for making a super junction power device, inwhich the steps of forming a floating island of a second conductive typeand a pillar of the second conductive type may be optional, depending onactual needs, and embodiments may be illustrated below.

First Embodiment

Please refer to FIG. 2 which shows a process flow chart of making asuper junction power device having both the floating island of thesecond conductive type and the pillar of the second conductive typeaccording to the present embodiment. Please also refer to FIGS. 3-5 forperspective views of a structure of the formed super junction powerdevice.

In the present embodiment, impurity of a second conductive type may beimplanted directly into an epitaxial layer of a first conductive type toform the floating island of the second conductive type and the pillar ofthe second conductive type with the same width successively throughadding a super junction mask after forming an epitaxial layer of thefirst conductive type. Multiple epitaxial processes and deep trenchetching process may not be needed. Therefore, the new process forforming super junction structure is simple, the cost is low, and theyield and reliability are high.

Please note that in the present embodiment the first conductive type isn type, and the second conductive type is p type, and in anotherembodiment the first conductive type may be p type, and the secondconductive type may be n type. No more limitation is needed here.

According to FIG. 2 , the formation process comprises steps of:

providing a substrate of a first conductive type 101;

forming an epitaxial layer of the first conductive type 102 on thesubstrate of the first conductive type 101;

forming a super junction mask on the surface of the epitaxial layer ofthe first conductive type 102;

through the super junction mask, implanting an impurity of a secondconductive type in the epitaxial layer of the first conductive type 102to form the floating island of the second conductive type 106,positioned in the epitaxial layer of the first conductive type 102, anda top surface and a bottom surface of the floating island of the secondconductive type 106 being in mutual contact with the epitaxial layer ofthe first conductive type 102;

through the super junction mask, implanting an impurity of the secondconductive type in the epitaxial layer of the first conductive type 102to form the pillar of the second conductive type 107, positioned in theepitaxial layer of the first conductive type 102 and right above thefloating island of the second conductive type 106;

forming trench gate structures in the epitaxial layer of the firstconductive type 102, the trench gate structures comprising a gate oxidelayer 108 and a gate conductive layer 109;

through a well mask, forming a well of a second conductive type 103 inthe epitaxial layer of the first conductive type 102 between the trenchgate structures, the well of the second conductive type 103 beingpositioned on the pillar of the second conductive type 107 and in mutualcontact with the pillar of the second conductive type 107;

through a source mask, forming a source of the first conductive type 104in the well of the second conductive type 103;

through a contact mask, forming a contact structure 105 passing throughthe source of the first conductive type 104 and in mutual contact withthe well of the second conductive type 103.

Specifically, at first, the substrate of the first conductive type 101is provided. The material of the substrate of the first conductive type101 may be doped semiconductor materials such as silicon (Si),silicon-germanium (SiGe), gallium nitride (GaN) or silicon carbide(SiC).

Then, on the substrate of the first conductive type 101, the epitaxiallayer of the first conductive type 102 is formed through epitaxial (epi)growth.

Then, the super junction mask is formed on the epitaxial layer of thefirst conductive type 102.

Specifically, on a surface of the epitaxial layer of the firstconductive type 102, a layer of hard mask material may be deposited. Thedeposition may be performed with but not limited to chemical vapordeposition. The layer of hard mask material may be and not limited to alayer of silicon dioxide. Then, on a surface of the layer of hard maskmaterial, both the floating island of the second conductive type 106 andthe pillar of the second conductive type 107 may be formed through alithography process, a dry etching process dry-etching the layer of hardmask material with a photoresist layer as etching mask that forms thesuper junction mask having the floating island of the second conductivetype 106 and the pillar of the second conductive type 107.

Then, through the super junction mask, impurity of the second conductivetype is implanted into the epitaxial layer of the first conductive type102 to form the floating island of the second conductive type 106. Then,through the floating island of the second conductive type 106, when thepower device is in open state (or off-state), the charge sharing effectof the drift region of the epitaxial layer of the first conductive type102 can result in effectively reduced doping level, so as to raise thebreakdown voltage and decrease both Miller capacitance and inputcapacitance of the power device. The floating island of the secondconductive type 106 allows the drift region of the epitaxial layer ofthe first conductive type having higher doping concentration, so thatthe on-state resistance of the device can be lower.

Then, through the super junction mask, impurity of the second conductivetype is implanted in to the epitaxial layer of the first conductive type102 to form the pillar of the second conductive type 107. Through thepillar of the second conductive type 107, when the power device is inopen state (or off-state), the charge sharing effect of the drift regionof the epitaxial layer of the first conductive type 102 can result ineffectively reduced doping level, so as to raise the breakdown voltageand decrease both Miller capacitance and input capacitance of the powerdevice. The pillar of the second conductive type 107 allows the driftregion of the epitaxial layer of the first conductive type having higherdoping concentration, so that the on-state resistance of the device canbe lower.

The sequence to form the floating island of the second conductive type106 and the pillar of the second conductive type 107 may beinter-changeable. The doping concentration of the floating island of thesecond conductive type 106 and the pillar of the second conductive type107 may be the same. The dopant may not be limited to B11. Because thefloating island of the second conductive type 106 and the pillar of thesecond conductive type 107 are formed with the same super junction maskin the present embodiment, the floating island of the second conductivetype 106 and the pillar of the second conductive type 107 have the samewidth.

In an example, a thickness range of the epitaxial layer of the firstconductive type 102 between the formed floating island of the formedsecond conductive type 106 and the pillar of the second conductive type107 is greater than 0.1 μm. A pnp triode (i.e. parasitic bipolartransistor) is formed between the formed floating island of the formedsecond conductive type 106 and the pillar of the second conductive type107; this parasitic pnp bipolar structure may further reduce theon-state resistance of an IGBT device.

Then, the trench gate structure may be formed in the epitaxial layer ofthe first conductive type.

Specifically, the trench gate structure may eliminate unit area of thepower device, in which the step of forming the trench gate structure maycomprise:

etching the epitaxial layer of the first conductive type 102 to formgate trenches;

performing a thermal oxidation process to grow a layer of the gate oxidelayer 108 covering a bottom and a side wall of the gate trenches on asurface of the gate trenches;

depositing polysilicon in the gate trenches to form the gate conductivelayer 109;

wherein the trench gate structure may facilitate reduce unit area of thepower device, the method of forming the trench gate structure may not belimited to what is disclosed here, a split gate may be chosen dependingon the need, and process and structure may not be limited to what isdisclosed here.

Then, through the well mask, the well of a second conductive type 103was formed in the epitaxial layer of the first conductive type 102between the trench gate structures. The well of a second conductive type103 was positioned on the pillar of the second conductive type 107 andin mutual contact with the pillar of the second conductive type 107.

Then, through the source mask, the source of the first conductive type104 is formed in the well of the second conductive type 103.

Then, through the contact mask, the contact structure 105 is formedpassing through the source of the first conductive type 104 and inmutual contact with the well of the second conductive type 103.

Specifically, as shown in FIG. 3 , in the present embodiment, thecontact structure 105 is formed with implanting the impurity of thesecond conductive type in the well of the second conductive type 103 toform the short-circuit connection to the source of the first conductivetype 104, but not limited to what is disclosed here. The contactstructure 105 may be trench gate structure comprising a contact regionof the second conductive type and a metal contact region. The contactregion of the second conductive type may be positioned in the contactregion of the second conductive type 103. The metal contact region, suchas metal W, may be passing through the source of the first conductivetype 104 in mutual contact with the contact region of the secondconductive type. As such, the on-state resistance may be furtherreduced, and area for the contact structure may be reduced, comparedwith traditional planar contact structure. The trench gate structurewill be introduced in a greater detail in the following embodiments.

Then, as shown in FIG. 4 , more steps of forming an interlayerdielectric layer 110, a source metal layer 111 and a drain metal layer112 may be comprised to form a VDMOSFET device, in which the order ofthe steps may be varied and the gate structure is known as planar type.

For example, one more step of forming a buffer layer of the firstconductive type at the bottom surface of the epitaxial layer of thefirst conductive type 102 may be comprised.

Specifically, the doping concentration of the buffer layer of the firstconductive type may be between that of the substrate of the firstconductive type 101 and the epitaxial layer of the first conductive type102 for achieving high BV; so as to avoid from the dopant atomsredistribution by a high temperature process. Therefore, the breakdownvoltage of the super junction power device due to doping profileredistribution in the epitaxial layer of the first conductive type 102may be prevented, and the problem of tail current during the deviceswitching off may also be solved with the substrate of the firstconductive type 101.

Please refer to FIG. 5 . The present embodiment also provides a methodof making an IGBT device. The difference between the method of making aVDMOSFET device in FIG. 4 and the method of FIG. 5 is an additional stepof making an additional implanted layer of the second conductive type113 between the drain metal layer 112 and the epitaxial layer of thefirst conductive type 102. Specifically, the substrate of the firstconductive type 101 may be removed with the backside grinding or CMP andthe implanted layer of the second conductive type 113 may be formed withbut not limited to implanting the impurity of the second conductivetype.

Please refer to FIG. 3 . The present embodiment also provides a superjunction power device, which may be made with but not limited to one ofthe aforesaid methods.

Specifically, the super junction power device may comprise the epitaxiallayer of a first conductive type 102, the trench gate structures, thewell of a second conductive type 103, the source of the first conductivetype 104, a contact structure 105, the floating island of the secondconductive type 106 and the pillar of the second conductive type 107, inwhich the well of a second conductive type 103 is positioned in theepitaxial layer of the first conductive type 102, the source of thefirst conductive type 104 is positioned in the well of the secondconductive type 103, the trench gate structures are positioned in theepitaxial layer of the first conductive type 102, the trench gatestructures comprise the gate oxide layer 108 and the gate conductivelayer 109, and the trench gate structures are passing through the sourceof the first conductive type 104 and the well of a second conductivetype 103; the contact structure 105 is passing through the source of thefirst conductive type 104 and in mutual contact with the well of thesecond conductive type 103, the floating island of the second conductivetype 106 is positioned in the epitaxial layer of the first conductivetype 102 and the top surface and the bottom surface of the floatingisland of the second conductive type 106 are in mutual contact with theepitaxial layer of the first conductive type 102, the pillar of thesecond conductive type 107 is positioned in the epitaxial layer of thefirst conductive type 102 and right above the floating island of thesecond conductive type 106 and in mutual contact with the well of thesecond conductive type 103, and the floating island of the secondconductive type 106 and the pillar of the second conductive type 107have the same width.

Because the super junction power device of the present invention hasboth the floating island of the second conductive type 106 and thepillar of the second conductive type 107, in open state (off state),both the floating island of the second conductive type 106 and thepillar of the second conductive type 107 may facilitate the chargesharing effect in the drift region of the epitaxial layer of the firstconductive type 102, so as to raise the breakdown voltage of the deviceand decrease both Miller capacitance and input capacitance; and in onstate, both the floating island of the second conductive type 106 andthe pillar of the second conductive type 107 allow the drift region ofthe epitaxial layer of the first conductive type 102 having higherdoping concentration to significantly increase current conducting anddecrease an on-state resistance. The additional parasitic pnp bipolarstructure in the epitaxial layer of the first conductive type 102 canfurther decrease the on-state resistance of a IGBT device.

For example, a thickness range of the epitaxial layer of the firstconductive type 102 between the floating island of the second conductivetype 106 and the pillar of the second conductive type 107 is greaterthan 0.1 μm, such as 1 μm, 5 μm.

For example, the contact structure 105 may comprise a metal contactregion, the metal contact region may be positioned at a contact regionof the second conductive type in the well of the second conductive type103, passing through the source of the first conductive type 104 and inmutual contact with the contact region of the second conductive type.

For example, a buffer layer of the first conductive type may be formedat the bottom surface of the epitaxial layer of the first conductivetype 102 to prevent from the re-distribution of dopant atoms of thesubstrate of the first conductive type 101 diffusing into the epitaxiallayer of the first conductive type 102 in a high temperature processthrough the buffer layer of the first conductive type. The buffer layerhelps to prevent from the degradation of breakdown voltage of the superjunction power device, and also solve the problem of tail current duringdevice switching off.

For example, an implanted layer of the second conductive type may beformed at the bottom surface of the epitaxial layer of the firstconductive type 102.

Specifically, as shown in FIG. 4 , the VDMOSFET may be formed furtherwith the interlayer dielectric layer 110, the source metal layer 111 andthe drain metal layer 112. Please refer to FIG. 5 , which shows that anadditional implanted layer of the second conductive type 113 may beadded between the drain metal layer 112 and the epitaxial layer of thefirst conductive type 102 to form an IGBT device. Further, the structureof the gate may not be limited to planar type, but also a trench type,or split gate.

Second Embodiment

Please refer to FIG. 6 . The present embodiment also provides a methodof making another super junction power device, which has both thefloating island of a second conductive type and a pillar of the secondconductive type. FIGS. 7-9 show perspective views of a structure of thesuper junction power device. The difference between the first and secondembodiments is that, in the present embodiment, impurity of the secondconductive type may be implanted to an epitaxial layer of a firstconductive type through a well mask before or after forming a well ofthe second conductive type to form the floating island of the secondconductive type and the pillar of the second conductive type which havethe same width as that of the well of the second conductive typesuccessively.

In the present embodiment, directly through the well mask, the impurityof the second conductive type may be implanted into the epitaxial layerof the first conductive type to sequentially form the floating island ofthe second conductive type and the pillar of the second conductive type.No additional mask is needed either. Therefore, the formation process issimple, the cost is low and yield and reliability are high.

Please note that in the present embodiment, the first conductive type isn type, and the second conductive type is p type, and in anotherembodiment, the first conductive type may be p type, and the secondconductive type may be n type.

Please refer to FIG. 6 which shows specific steps of the making processincluding:

providing a substrate of the first conductive type 201;

forming an epitaxial layer of the first conductive type 202 on thesubstrate of the first conductive type 201;

forming trench gate structures in the epitaxial layer of the firstconductive type 202, the trench gate structures comprising a gate oxidelayer 208 and a gate conductive layer 209;

forming a well mask;

through the well mask, forming the floating island of the secondconductive type 206 with implanting the impurity of the secondconductive type in the epitaxial layer of the first conductive type 202,the floating island of the second conductive type 206 being positionedin the epitaxial layer of the first conductive type 202, and a topsurface and a bottom surface of the floating island of the secondconductive type 206 being in mutual contact with the epitaxial layer ofthe first conductive type 202;

through the well mask, forming the pillar of the second conductive type207 with implanting the impurity of the second conductive type in theepitaxial layer of the first conductive type 202, the pillar of thesecond conductive type 207 being positioned in the epitaxial layer ofthe first conductive type 202 and no deeper than the bottom of gatetrench and right above the floating island of the second conductive type206;

through the well mask, forming a well of the second conductive type 203in the epitaxial layer of the first conductive type 202 between thetrench gate structures, the well of the second conductive type 103 beingin mutual contact with the pillar of the second conductive type 207;

through a source mask, forming a source of the first conductive type 204in the well of the second conductive type 203;

through a contact mask, forming a contact structure 205, passing throughthe source of the first conductive type 204 and in mutual contact withthe well of the second conductive type 203.

Specifically, through the trench gate structures, the unit area of thepower device can be reduced. The trench gate structures may be splitgate depending on the need and the forming process and structure may notbe limited to what is disclosed here. the order to form the floatingisland of the second conductive type 206 and the pillar of the secondconductive type 207 through the well mask may not be limited to thepresent embodiment. The order may be varied depending on the actualneeds; for example, the second conductive type 206 and the pillar of thesecond conductive type 207 may be formed after forming the well of thesecond conductive type 203. Please refer to the first embodiment for thedetailed function of the second conductive type 206 and the pillar ofthe second conductive type 207.

For example, a thickness range of the epitaxial layer of the firstconductive type 202 between the formed floating island of the formedsecond conductive type 206 and the pillar of the second conductive type207 is greater than 0.1 μm, such as 1 μm, 5 μm, but not limited to thesevalues.

For example, the contact structure is formed by implanting the impurityof the second conductive type into the well of the second conductivetype 203, so as to form a short-circuit connection to the source of thefirst conductive type 204. However, the contact structure is not limitedto what is disclosed here, and the contact structure may be formed withtrench type contact structure which will be introduced in the followingembodiment.

Then, as shown in FIG. 8 , more steps of forming an interlayerdielectric layer 210, a source metal layer 211 and a drain metal layer212 may be comprised to form a VDMOSFET device. The order of these stepsmay be varied depending on actual need.

For example, one more step of forming a buffer layer of the firstconductive type at the bottom surface of the epitaxial layer of thefirst conductive type 202 may be comprised.

Please refer to FIG. 9 . The present embodiment also provides a methodof making an IGBT device. The difference between the method of making aVDMOSFET device in FIG. 8 and the method of FIG. 9 is an additional stepof making an additional implanted layer of the second conductive type213 between the drain metal layer 212 and the epitaxial layer of thefirst conductive type 202. Specifically, the substrate of the firstconductive type 201 may be removed with backside grinding or CMP and theimplanted layer of the second conductive type 213 may be formed with butnot limited to implanting the impurity of the second conductive type.

Please refer to FIG. 7 . The present embodiment also provides a superjunction power device, which may be made with but not limited to one ofthe aforesaid methods.

Specifically, the super junction power device may comprise the epitaxiallayer of the first conductive type 202, trench gate structures, the wellof the second conductive type 203, the source of the first conductivetype 204, the contact structure 205, the floating island of the secondconductive type 206 and the pillar of the second conductive type 207, inwhich the well of the second conductive type 203 is positioned in theepitaxial layer of the first conductive type 202 no deeper than thebottom of gate trench, the source of the first conductive type 204 ispositioned in the well of a second conductive type 203, the trench gatestructures are positioned in the epitaxial layer of the first conductivetype 202, including the gate oxide layer 208 and the gate conductivelayer 209, and passing through the source of the first conductive type204 and the well of the second conductive type 203, the contactstructure 205 is passing through the source of the first conductive type204 and in mutual contact with the well of the second conductive type203, the floating island of the second conductive type 206 is positionedin the epitaxial layer of the first conductive type 202 and the topsurface and the bottom surface of the floating island of the secondconductive type 206 are in mutual contact with the epitaxial layer ofthe first conductive type 202, the pillar of the second conductive type207 is positioned in the epitaxial layer of the first conductive type202 no deeper than the bottom of gate trench and right above thefloating island of the second conductive type 206 and in mutual contactwith the well of the second conductive type 203, and the floating islandof the second conductive type 206 and the pillar of the secondconductive type 207 have the same width as that of the well of thesecond conductive type 203.

For example, a thickness range of the epitaxial layer of the firstconductive type 202 between the floating island of the second conductivetype 206 and the pillar of the second conductive type 207 is greaterthan 0.1 μm, such as 1 μm, 5 μm, but not limited to these values.

For example, the contact structure 205 may comprise a metal contactregion which is positioned at a contact region of the second conductivetype in the well of the second conductive type 203, passing through thesource of the first conductive type 204 and in mutual contact with thecontact region of the second conductive type.

For example, a buffer layer of the first conductive type may be formedat the bottom surface of the epitaxial layer of the first conductivetype 202.

For example, an implanted layer of the second conductive type may beformed at the bottom surface of the epitaxial layer of the firstconductive type 202.

Specifically, as shown in FIG. 8 , the VDMOSFET may be formed furtherwith the interlayer dielectric layer 210, the source metal layer 211 andthe drain metal layer 212. Please refer to FIG. 9 , which shows that anadditional implanted layer of the second conductive type 213 may beadded between the drain metal layer 212 and the epitaxial layer of thefirst conductive type 202 to form the IGBT device. Further, thestructure of the gate may not be limited to planar type, but also trenchtype or split gate.

Third Embodiment

Please refer to FIG. 10 . The present embodiment also provides a methodof making yet another super junction power device, which has both afloating island of a second conductive type and a pillar of the secondconductive type. FIGS. 10-13 show perspective views of a structure ofthe super junction power device. The difference between the first andsecond embodiments is that, in the present embodiment, impurity of thesecond conductive type may be implanted into an epitaxial layer of afirst conductive type directly through a contact mask before or afterforming a contact structure to form the floating island of the secondconductive type and the pillar of the second conductive type which havethe same width as that of the contact structure successively. Thecontact structure applies trench contact structures, i.e. comprising acontact region of the second conductive type and a metal contact region,and the buffer layer of the first conductive type is formed at a bottomsurface of the epitaxial layer of the first conductive type.

In the present embodiment, the impurity of the second conductive typemay be implanted directly to the epitaxial layer of the first conductivetype to form the floating island of the second conductive type and thepillar of the second conductive type successively through the contactmask directly. No additional mask is needed either. Therefore, theformation process is simple, the cost is low and yield and reliabilityare high. Preferably, the floating island of the second conductive typeand the pillar of the second conductive type may be formed after formingthe contact mask and forming the contact structure to perform an annealprocess for the floating island of the second conductive type and thepillar of the second conductive type simultaneously when performing ananneal step for the contact structure. As such, the complexity ofprocess may be declined and the cost may be reduced.

Please note that in the present embodiment, the first conductive type isn type, and the second conductive type is p type, and in anotherembodiment, the first conductive type may be p type, and the secondconductive type may be n type.

Please refer to FIG. 10 which shows specific steps of the making processincluding:

providing a substrate of the first conductive type 301;

forming an epitaxial layer of the first conductive type 302 on thesubstrate of the first conductive type 301;

forming trench gate structures in the epitaxial layer of the firstconductive type 302, the trench gate structures comprising a gate oxidelayer 308 and a gate conductive layer 309;

through a well mask, forming a well of the second conductive type 303 inthe epitaxial layer of the first conductive type 302 between the trenchgate structures;

through a source mask, forming a source of the first conductive type 304in the well of the second conductive type 303;

forming the contact mask;

through the contact mask, forming a floating island of the secondconductive type 306 with implanting the impurity of the secondconductive type in the epitaxial layer of the first conductive type 302,the floating island of the second conductive type 306 being positionedin the epitaxial layer of the first conductive type 302, and a topsurface and a bottom surface of the floating island of the secondconductive type 306 being in mutual contact with the epitaxial layer ofthe first conductive type 302;

through the contact mask, forming the pillar of the second conductivetype 307 with implanting the impurity of the second conductive type inthe epitaxial layer of the first conductive type 302, the pillar of thesecond conductive type 307 being positioned in the epitaxial layer ofthe first conductive type 302, right above the floating island of thesecond conductive type 306 and in mutual contact with the well of thesecond conductive type 303;

through the contact mask, forming the contact structure 305, passingthrough the source of the first conductive type 304 and in mutualcontact with the well of the second conductive type 303.

Specifically, through the trench gate structures, unit area of powerdevices may be reduced. The trench gate structure may be split gatestructure but related process and structure are not limited to what isdisclosed here.

Specifically, steps of forming the contact structure 305 may comprise:

through the contact mask, etching the source of the first conductivetype 304 to form a contact trench passing through the source of thefirst conductive type 304;

through the contact mask, forming the contact region of the secondconductive type 3051 with implanting of the impurity of the secondconductive type in the well of the second conductive type 303;

through the contact mask, forming the metal contact region 3052 fillingin the contact trench, the metal contact region 3052 being in contactwith the contact region of the second conductive type 3051 2.

Specifically, the pillar of the second conductive type 307 is in mutualcontact with the contact region of the second conductive type 3051, andthe material of the metal contact region 3052 may be metal W to form theshort-circuit connection to the source of the first conductive type 304to further decrease the on-state resistance and reduce area of thecontact structure, compared with traditional planar contact structure.Preferably, the floating island of the second conductive type and thepillar of the second conductive type may be formed after forming thecontact mask and forming the contact structure 305, so as to perform ananneal process for the floating island of the second conductive type 306and the pillar of the second conductive type 307 simultaneously whenperforming an anneal step for the contact region of the secondconductive type 3051. As such, the complexity of process may be declinedand the cost may be reduced. The order to form the floating island ofthe second conductive type 306 and the pillar of the second conductivetype 307 through the contact mask may not be limited to the presentembodiment. The order may be varied depending on the actual needs.Please refer to the first embodiment for the detailed function of thefloating island of the second conductive type 306 and the pillar of thesecond conductive type 307.

For example, a thickness range of the epitaxial layer of the firstconductive type 302 between the formed floating island of the formedsecond conductive type 306 and the pillar of the second conductive type307 is greater than 0.1 μm, such as 1 μm, 5 μm, but not limited to thesevalues.

Then, as shown in FIG. 12 , more steps of forming an interlayerdielectric layer 310, a source metal layer 311 and a drain metal layer312 may be comprised to form a VDMOSFET device, in which the order toperform the steps of forming the super junction power device may be notlimited but depend on the actual needs.

For example, one more step of forming a buffer layer of the firstconductive type 314 at the bottom surface of the epitaxial layer of thefirst conductive type 302 may be comprised. Specifically, through thebuffer layer of the first conductive type 314, the dopant atoms of thesubstrate of the first conductive type 301 may be prevented fromdiffusion into the epitaxial layer of the first conductive type 302 in ahigh temperature process; therefore, breakdown voltage of the superjunction power device is not degraded by the re-distribution of dopingconcentration of the epitaxial layer, The problem of tail current duringdevice switching off may also be solved.

Please refer to FIG. 13 . The present embodiment also provides a methodof making an IGBT device. The difference between the method of making aVDMOSFET device in FIG. 12 and the method of FIG. 13 is an additionalstep of making an additional implanted layer of the second conductivetype 313 between the drain metal layer 313 and the epitaxial layer ofthe first conductive type 302. Specifically, the substrate of the firstconductive type 301 may be removed by backside grinding or CMP and theimplanted layer of the second conductive type 313 may be formed with butnot limited to implanting the impurity of the second conductive type.

Please refer to FIG. 11 . The present embodiment also provides a superjunction power device, which may be made with but not limited to one ofthe aforesaid methods.

Specifically, the super junction power device may comprise the epitaxiallayer of the first conductive type 302, the trench gate structures, thewell of the second conductive type 303, the source of the firstconductive type 304, the contact structure 305, the floating island ofthe second conductive type 306 and the pillar of the second conductivetype 307, in which the well of the second conductive type 303 ispositioned in the epitaxial layer of the first conductive type 302, thesource of the first conductive type 304 is positioned in the well of asecond conductive type 303, the trench gate structures are positioned inthe epitaxial layer of the first conductive type 302, including the gateoxide layer 308 and the gate conductive layer 309, and passing throughthe source of the first conductive type 304 and the well of the secondconductive type 303, the contact structure 305 is passing through thesource of the first conductive type 304 and in mutual contact with thewell of the second conductive type 303, the floating island of thesecond conductive type 306 is positioned in the epitaxial layer of thefirst conductive type 302 and the top surface and the bottom surface ofthe floating island of the second conductive type 306 are in mutualcontact with the epitaxial layer of the first conductive type 302, thepillar of the second conductive type 307 is positioned in the epitaxiallayer of the first conductive type 302 and right above the floatingisland of the second conductive type 306 and in mutual contact with thewell of the second conductive type 303, and the floating island of thesecond conductive type 306 and the pillar of the second conductive type307 have the same width as that of the contact structure 305.

For example, the contact structure 305 may comprise a metal contactregion 3052 which is positioned at a contact region of the secondconductive type 3051 in the well of the second conductive type 303,passing through the source of the first conductive type 304 and inmutual contact with the contact region of the second conductive type3051. The pillar of the second conductive type 307 is in mutual contactwith the contact region of the second conductive type 3051.

For example, a thickness range of the epitaxial layer of the firstconductive type 302 between the floating island of the second conductivetype 306 and the pillar of the second conductive type 307 is greaterthan 0.1 μm, such as 1 μm, 5 μm, but not limited to these values,

For example, a buffer layer of the first conductive type 314 may beformed at the bottom surface of the epitaxial layer of the firstconductive type 302.

For example, an implanted layer of the second conductive type 313 may beformed at the bottom surface of the epitaxial layer of the firstconductive type 302.

Specifically, as shown in FIG. 12 , the VDMOSFET may be formed furtherwith the interlayer dielectric layer 310, the source metal layer 311 andthe drain metal layer 312. Please refer to FIG. 13 , which shows that anadditional implanted layer of the second conductive type 313 may beadded between the drain metal layer 312 and the epitaxial layer of thefirst conductive type 302 to form the IGBT device. Further, thestructure of the gate may not be limited to planar type, but also trenchtype or split gate.

To sum up, according to the super junction power device and the methodof making the same of the present invention, when making a superjunction power device, impurity of the second conductive type may beimplanted into the epitaxial layer of the first conductive type to formthe floating island of the second conductive type and the pillar of thesecond conductive type successively through adding a super junction maskafter forming the epitaxial layer of the first conductive type, directlythrough the well mask before or after forming the well of the secondconductive type, and directly through the contact mask before or afterforming the contact structure. Therefore, the formation process issimple, the cost is low and yield and reliability are high. Because thesuper junction power device of the present invention has both thefloating island of the second conductive type and the pillar of thesecond conductive type, in open state (off state), both the floatingisland of the second conductive type and the pillar of the secondconductive type may facilitate charge sharing effect of the drift regionof the epitaxial layer of the first conductive type, so as to raise thebreakdown voltage and decrease both Miller capacitance and inputcapacitance; and in on state, both the floating island of the secondconductive type and the pillar of the second conductive type allow thedrift region of the epitaxial layer of the first conductive type havinghigher doping concentration to significantly increasing currentconduction and decrease an on-state resistance of a VDMOSFET device, soas to form an additional parasitic bipolar transistor in the epitaxiallayer of the first conductive type to further decrease the on-stateresistance of a IGBT device.

It is to be understood that these embodiments are not meant aslimitations of the invention but merely exemplary descriptions of theinvention with regard to certain specific embodiments. Indeed, differentadaptations may be apparent to those skilled in the art withoutdeparting from the scope of the annexed claims. In all instances, thescope of such claims shall be considered on their own merits in light ofthis disclosure, and such claims accordingly define the invention(s),and their equivalents or variations, that are protected thereby.

What is claimed is:
 1. A method of making a super junction power device,characterized by, comprising: forming an epitaxial layer of a firstconductive type; forming trench gate structures in the epitaxial layerof the first conductive type, the trench gate structures comprising agate oxide layer and a gate conductive layer; through a well mask,forming a well of a second conductive type in the epitaxial layer of thefirst conductive type between the trench gate structures; through asource mask, forming a source of the first conductive type in the wellof the second conductive type; through a contact mask, forming a contactstructure passing through the source of the first conductive type and inmutual contact with the well of the second conductive type; forming afloating island of the second conductive type, positioning in theepitaxial layer of the first conductive type, and a top surface and abottom surface of the floating island of the second conductive typebeing in mutual contact with the epitaxial layer of the first conductivetype; forming a pillar of the second conductive type, positioning in theepitaxial layer of the first conductive type and right above thefloating island of the second conductive type, and being in mutualcontact with the well of the second conductive type.
 2. The method ofmaking the super junction power device according to claim 1,characterized by: wherein a super junction mask is formed on a surfaceof the epitaxial layer of the first conductive type after forming theepitaxial layer of the first conductive type, and through the superjunction mask, impurity of the second conductive type is implanted intothe epitaxial layer of the first conductive type to form the floatingisland of the second conductive type and the pillar of the secondconductive type successively.
 3. The method of making the super junctionpower device according to claim 1, characterized by: wherein before orafter forming the well of the second conductive type, through the wellmask, impurity of the second conductive type is implanted into theepitaxial layer of the first conductive type to form the floating islandof the second conductive type and the pillar of the second conductivetype successively.
 4. The method of making the super junction powerdevice according to claim 1, characterized by: wherein before or afterforming the contact structure, through the contact mask, impurity of thesecond conductive type is implanted into the epitaxial layer of thefirst conductive type to form the floating island of the secondconductive type and the pillar of the second conductive typesuccessively.
 5. The method of making the super junction power deviceaccording to claim 1, characterized by: wherein a thickness range of theepitaxial layer of the first conductive type between the floating islandof the second conductive type and the pillar of the second conductivetype is greater than 0.1 μm.
 6. The method of making the super junctionpower device according to claim 1, characterized by: wherein the step offorming the contact structure comprises: through the contact mask,etching the source of the first conductive type and forming a contacttrench passing through the source of the first conductive type; throughthe contact mask, implanting impurity of the second conductive type intothe well of the second conductive type to form a contact region of thesecond conductive type; through the contact mask, forming a metalcontact region filling in the contact trench, and the metal contactregion being in mutual contact with the contact region of the secondconductive type.
 7. The method of making the super junction power deviceaccording to claim 1, characterized by: wherein the first conductivetype is n type, and the second conductive type is p type; or the firstconductive type is p type, and the second conductive type is n type. 8.The method of making the super junction power device according to claim1, characterized by: further comprising a step of forming a buffer layerof the first conductive type at the bottom surface of the epitaxiallayer of the first conductive type.
 9. The method of making the superjunction power device according to claim 1, characterized by: furthercomprising a step of forming an implanted layer of the second conductivetype at the bottom surface of the epitaxial layer of the firstconductive type.